高效液相色谱及联用技术在砷形态分析中的应用

砷与人类的生活息息相关,是环境中存在的一种极为重要的非金属元素。由于不同形态的砷其毒性各不同,因此无论对环境样品、食品、药物还是对人体的体液进行砷的形态分析都是至关重要的。高效液相色谱因具有较高的分离能力而被广泛地应用于砷形态的分离研究中。随着对分析灵敏度与准确度要求的不断提高,作为砷形态分析的检测器不断发展,不同的联用技术也日益完善。其中,电感耦合等离子体质谱法以其极高的灵敏度、多元素同时检测能力、极宽的动态范围以及同位素比检测能力而被成功地作为高效液相色谱的检测器,广泛地应用于砷的形态分析中。     

Electrical and XPS studies of 100 MeV Si ion irradiated Pd/n-GaAs devices

The effect of Swift Heavy Ion (100 MeV Si⁷⁺) irradiation on electronic-transport of Pd/n-GaAs devices has been studied by I–V and C–V techniques. The chemical compositions of the interface have been studied by XPS/EDAX techniques. It is observed that the irradiated devices show a reduction in current and capacitance by few orders of magnitude. The C–V characteristics show a change in conductivity type from n- to p-type after the irradiation. On hydrogenation, the irradiated devices show a capacitance peak in C–V characteristics, which has been ascribed to As vacancies. The XPS studies of these devices, for various etching durations, show that the ratio of As:Ga has reduced after the irradiation, which indicates the formation of irradiation-induced As vacancies. This reduction in As:Ga ratio is also confirmed by EDAX measurement. The observed conductivity type change from n- to p-type (on the irradiation) seems to be due to the change of substitutional sites of dopant silicon atoms from Ga to As sites due to the irradiation-induced As vacancies.     

Charge Transfer and Chemical Hardness along a Substitution Path in Metastable Au‐Sb Alloys

In the present study the synthesis of metastable alloys of the noble metal Au and the semimetal Sb is realized by using high pressure techniques. The influence of Au on bulk Sb is shown experimentally by stepwise substitution. In addition to the effect of the most electronegative noble metal on Pauling's scale in the binary Au‐Sb phases, some ternary compounds with In, Sn, As, and Te in addition to Au and Sb are discussed. The experiments are planned to obtain a better knowledge on the reasons for building up a simple cubic Sb partial lattice, and their crystallographic results are used to construct model structures for new electronic structure calculations from first principles on the metastable π‐phases. Using the LCAO‐CO ansatz and density‐functional methods, we study total energies, band structures, densities of states and charge transfer properties according to Bader's method by integrating zero flux surfaces. Finally, from electronic band structure analysis, the quantities “chemical potential” μ, and “chemical hardness”, η, are derived according to the original ideas of Pearson and Parr and are applied to solid state problems using special points of the Brillouin zones within a band structure approximation for the first time. The results are shown to support the experimental findings about the substitution path within the system Au‐Sb.     

Observation of sequential excited-to-excited states resonant tunneling in weakly coupled superlattices with wide quantum wells

The sequential excited-to-excited state resonant tunneling effect was observed in weakly coupled long-period superlattices resulting in additional negative differential conductivity resonances in multistable current–voltage characteristics. The results obtained show the evidence of the highly nonequilibrium distribution of carriers over subbands with energies below the optical phonon energy in superlattices. A new type of electric field domains, due to resonant tunneling between excited subbands in adjacent wells, is considered, and experimental evidencies of such a domain's existence are given.     

Franz–Keldysh oscillations at the miniband edge in a GaAs/AlxGa1 −xAs superlattice

We have systematically measured the electroreflectance spectra of a GaAs (7.0 nm)/Al_0.1Ga_0.9As (3.5 nm) superlattice at various electric fields to investigate Franz–Keldysh (FK) oscillations. In the low-field regime, we clearly observe the FK oscillations toward the low-energy side of theM₁critical point (mini-Brillouin-zone edge). As the electric field is increased, the direction of the FK oscillations is reversed, then the oscillations disappear. The change of the oscillation direction correlates with the transformation of the electronic structures from the miniband to the Stark-ladder states in the Wannier-Stark localization. We discuss these experimental results on the basis of a theory of the FK oscillations and envelope-function forms calculated by a transfer matrix method with Airy functions.     

电感耦合等离子体质谱法测定苎麻不同部位的铬、砷、镉、铅4种重金属元素含量

采用硝酸-双氧水-氢氟酸体系对苎麻不同部位样品进行微波消解,通过智能控温加热器赶酸,利用电感耦合等离子体质谱(ICP-MS)检测苎麻不同部位的铬、砷、镉及铅含量.结果表明:方法操作简便,分析速度快,灵敏度及线性较好,各元素的检出限为~(52)Cr 0.05 mg/kg、~(75)As 0.02 mg/kg、~(111)Cd 0.02 mg/kg、~(208)Pb 0.03 mg/kg,线性范围分别为Cr 0.5~50 mg/kg、As和Cd均为0.1~12.5 mg/kg、Pb 0.2~25 mg/kg.方法精密度和稳定性较好,试验回收率在80.0%~125%之间.初步判断苎麻不同部位4种重金属元素的高低水平,以及苎麻对土壤中的重金属有一定吸附作用.     

HG-AFS法连续测定锌精矿中砷锑铋锡的不确定度分析

对HG AFS法连续测定锌精矿中砷、锑、铋、锡的不确定度进行了分析。根据建立的数学模型计算出各种不确定度的分量并将其合成,最后得出HG AFS法连续测定锌精矿中砷、锑、铋、锡的扩展不确定度。     

Screen Printed Carbon Electrode Modified with Poly(L‐Lactide) Stabilized Gold Nanoparticles for Sensitive As(III) Detection

Poly(L ‐lactide) stabilized gold nanoparticles (designated as PLA–Au^NP) with an average particle size of ca. 10 nm were used to modify a disposable screen‐printed carbon electrode (SPE) for the detection of As(III) by differential pulse anodic stripping voltammetry. Gold modification was evaluated by cyclic voltammetry, whereas scanning electron microscopy and transmission electron microscopy revealed the size and distribution of gold nanoparticles. The PLA–Au^NP/SPE was applied effectively to detect toxic As(III) in HCl medium. Under the optimal experimental conditions, a linear calibration curve up to 4 ppm with a detection limit (S/N=3) of 0.09 ppb was obtained. The sensitivity was good enough to detect As(III) at levels lower than the current EPA standard (10 ppb). Most importantly, the PLA–Au^NP/SPE can be tolerable from the interference of Cu, Cd, Fe, Zn, Mn, and Ni and hence provides a direct and selective detection method for As(III) in natural waters. Practical utility of the PLA–Au^NP/SPE was demonstrated to detect As(III) in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei‐Men).     

First order speciation of As using flow injection hydride generation atomic absorption spectrometry with in-situ trapping of the arsine in a graphite furnace

A simple method is described to distinguish between As species that react with sodium tetrahydroborate (III) to form AsH₃ and the naturally occurring As species that are unreactive. Results for this rudimentary or “first order” speciation scheme are reported for biological tissue, aquatic plant material, urine and natural water samples. Biological tissue and aquatic plant samples were briefly solubilized in a mixture of 50% nitric acid, no sample preparation was required for the urine or natural water samples. Organoarsenic species which do not react with sodium borohydride under acidic conditions such as arsenobetaine, arsenocholine and tetramethylarsenic, are converted to As(V) by on-line photo-oxidation or microwave heating in a mixture of 0.5 M NaOH and 0.05 M K₂S₂O₈. The sample is subsequently acidified, reduced with sodium borohydride and the generated arsine is trapped in a heated graphite furnace prior to atomization. The superior detection limit (0.14 ng) of the trapping technique permits the dilution of most types of samples, minimizing or eliminating interference effects. Without photolysis or microwave heating a combined result for As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is obtained. Results are reported for the first order speciation of As in a suite of certified reference materials (CRMs) including National Research Council (NRC) biological tissues and natural water samples, Community Bureau of Reference (BCR) aquatic plant materials and the National Institute of Standards and Technology (NIST) SRM 267ON urine sample. The determination of a non-hydride forming As fraction in untreated urine and natural water certified reference materials (CRMs) has revealed a species of As previously undetected in NRC seawater CRMs.     

[t-Bu2P]3P7 und (t-Bu2Sb)3P7 sowie Untersuchungen zur Bildung von Heptaphosphanen(3) mit PMe2-, PF2- und P(CF3)2-Gruppen

[t-Bu₂P]₃P₇ and (t-Bu₂Sb)₃P₇, as well as Investigations on the Formation of Heptaphosphanes (3) Containing PMe₂, PF₂, and P(CF₃)₂ Groups Tris(di-tert-butylphospha)heptaphosphanortricyclane (t-Bu₂P)₃P₇ 1 obtained by reacting Li₃P₇ · 3 DME with t-Bu₂PF forms yellow crystals. (t-Bu₂Sb)₃P₇ 2 produced similarly from t-Bu₂SbCl and Li₃P₇ · 3 DME didn't form crystals; it decomposes in a solution of toluene above ?10°C. Both compounds were identified by their ³¹P{¹H} NMR spectra, and 1 also by elemental analysis and single crystal structure determination (space group) P2₁/a, a = 1 712.0(9) pm, b = 1 105.1(7) pm, c = 1 854.0(10) pm, β = 94.96(4)°, Z = 4 formula units in the elementary cell). Attempts to synthesize (Me₂P)₃P₇ 3 , (F₂P)₃P₇ 4 and [(F₃C)₂P]₃P₇ 5 failed as dialkylchlorophosphanes as Me₂PCl e. g. with Li₃P₇ · 3 DME react under Li/Cl exchange, dialkylfluorophosphanes (except t-Bu₂PF) disproportionate, and neither PF₃ nor (F₃C)₂PBr with Li₃P₇ · 3 DME give the desired products 4 or 5 , resp.